Ventilation overcasts are commonly installed at various places in the entries (i.e., tunnels) in underground mines, such as coal mines, and are used to separate the intake and return air flows used to ventilate the mines. In general, such ventilation overcasts take the form of substantially air-tight bridges which permit the crossing of intake and return airways without interference.
Many different types of ventilation overcasts have been developed over the years and have been used with varying degrees of success. For example, ventilation overcasts have been constructed of tile, brick, stone, concrete, concrete blocks, steel panels, or combinations of the foregoing materials, with steel beams being used where necessary to provide additional support. Ventilation overcasts made from the foregoing materials typically require 2-6 days to construct, depending on the particular design and materials used. For example, overcasts fabricated from bricks or concrete blocks generally require 4-6 days to construct, while other designs utilizing primarily steel members may be constructed in less time, typically about 2-3 days.
The construction of such ventilation overcasts represents a substantial portion of the time, thus cost, required to develop and maintain the underground mine ventilation system. Consequently, devices and methods are always being sought which can reduce the time and/or cost required to acquire, set-up, and maintain the ventilation overcast. Toward this end, several different types of "quick assembly" ventilation overcasts have been developed in recent years which further reduce the time required for construction. While such "quick assembly" overcasts are being used more and more frequently, many still require at least one day (i.e., one work shift) to install.
One problem that may complicate the design and construction of ventilation overcasts is the degree of floor heave that may be expected in the mine. While some mines experience more floor heave than others, all mines experience at least some degree of floor heave. Heaving of the mine floor can compromise the air-tight construction of the overcast, causing intermixing of the return and intake air flows. Such intermixing of the return and intake air flows may violate applicable ventilation regulations and, in any event, represents an undesirable circumstance. Moreover, if the floor heave is excessive, it can result in structural damage to the overcast, possibly requiring that the overcast be repaired or even replaced before mining can continue.
Primarily in an effort to address the foregoing problems, ventilation overcasts have been developed which can compensate for a certain amount of floor heave. Unfortunately, the structure required to accommodate such floor heave tends to further increase the complexity, thus cost of the ventilation overcast. Furthermore, such accommodations usually require additional time to construct, thereby removing some of the advantages associated with quick assembly type of ventilation overcasts in which they may be utilized.